Joint, synovial fluid and cartilage Flashcards
What is a fibrous joint?
- Composed of collagen fibres and fibrous connective tissue
- The fibers have very high tensile strength
- Not much movement
Give examles of fibrous joints
□ Periodontal ligament
□ Cranial structures
□ Interosseous membranes
® Forearm and leg
What is a cartilagenous joint?
- A bit more mobile than the fibrous joints but not that mobile
- Primary cartilaginous (Synchondrosis)- only hyaline cartilage
□ Growth plate (growing long bones) - Secondary cartilaginous (symphysis)- hyaline and fibrocartilage
□ Intervertebral disks
What are the common features of synovial joints?
□ Synovial cavity (fluid-filled) □ Articular cartilage □ Fibrous capsule □ Synovial membrane □ Synovial fluid
Synovial joints may also contain… (that are not common features)
□ Articular disks
□ Ligaments
□ Bursae
® Fluid filled pillows that reduce friction around the joints
What are the different types of synoial joints (give an examle for each)?
- Synovial plane: Facet joints
- Synovial hinge: elbow joint
- Pivot joint: Radial ulnar joint
- Synovial condylar (ellipsoid): the radiocarpal joint
- Synovial saddle: between the traezium carale bone and the first metacaral bone
- Synovial ball and socket: shoulder joint
How do joints maintain stability?
○ Shape of articulating surfaces
○ Capsule and ligaments
○ Muscles
Describe the chondrocytes in the superficial/ tangential layer of articular cartilage
□ Flattened
□ Produces collagen and glycoproteins (e.g. lubricin)
Describe the chondrocytes in the
transitional layer of articular cartilage
□ Round
□ Produces proteoglycans such as aggrecan (which can bind water and keeps water in the articular cartilage)
Describe the change in collagen orientation in articular carilage
- Parallel in the superficial layer
- Oblique fibers in the transitional layer
- Vertical fibers in the deep layer
What percentage of young and healthy articular cartilage is water and why is this?
- > 75%
- Water is incompressible
- This allows the tissue to be protected from being compressed
What is the average thickness of articular cartilage in joints and why might it vary deending on the joint?
- 2-3mm
- It depends on the forces acting on the joint
- if it is not weight bearing then the joint doesn’t need as thick articular cartilage
- If when doing certain things the forces acting on the joint are very strong then the joint needs a thicker articular cartilage
What are glycoproteins?
- e.g. lubricin
- Proteins to which oligosaccharide chains are attached
- More a protein than a carbohydrate
- A very good lubricator
What are proteoglycans?
- e.g. aggrecan
- Proteins that are heavily glycosylated (a protein core to which one or more GAGs attached)
- Tend to be more carbohydrate than protein
What are glycosaminoglycans (GAGs)?
- e.g. hyaluronic acid
- Long unbranched polysaccharides, which are highly polar and thus attract water
- Makes the synovial fluid a bit more viscus making it a better lubricator
- It is part of molecules such as aggrecans
What are the properties of cartilage? (3 A’s)
○ Avascular
○ Aneural
○ Alymphatic
Where is synovial fluid produced?
○ Synovial fluid produced by synovial membrane (synovium) - Synoviocytes producing the fluid □ Type A ® Look like macrophages ® Remove debris ® Contribute to synovial fluid production □ Type B ® Fibroblast like ® Main producer of synovial fluid
Describe synovial fluid
○ Viscous fluid ○ Hyaluronic acid & lubricin ○ Fluid component (from blood plasma) ○ Small volumes (knee joint: ̴0.5 ml ) ○ Rapid turnover ( ̴2 hours)
What is the function of synovial fluid?
- Nutrition of cartilage (articular c., menisci/discs)
- Removal of waste products
- Lubrication → less friction → less wear
□ Boundary
® Glycoproteins such as lubricin bind to receptors on articular surfaces to form a thin film
□ Hydrodynamic (like aquaplaning)
® Surfaces kept apart by liquid pressure
® Viscosity changes with load and velocity of movement
□ Weeping
® Fluid that is present in the cartilage is squeezed out into the synovial cavity to increase fluid volume
® When you have high pressure acting on the joint you get weeping lubrication
What are bursae?
○ Made up of synovial membrane
○ Fluid-filled
○ In areas with a high level of friction
○ Reduced friction
What happens to the joints when aging?
○ Viscosity of synovial fluid increases
- Slower joint movements
- Reduced lubrication
○ Water content of cartilage decreases
- Reduced shock absorption due to the loss of the incompressible water
- Higher risk of damage
- Less protection of articular surfaces & increased risk of damage
○ Osteoarthritis
- Narrow disk
- Bone spur (osteophytes)
- Uncontrolled additional bone growth around the edges
